A device allowing nonreciprocal transmission, or in other words, transmission in one direction and blocking in the other), is a fundamental building block in information processing. Nonreciprocal transmission is sometimes referred to as the “diode effect”. In electrical system, nonreciprocal transmission has been realized in integrated circuits by a p-n junction in a semiconductor device, or in other words, a common diode.
However, in the field of optics, nonreciprocal transmission is inherently difficult to accomplish, due to the time-reversal symmetry of the light-matter interaction. Prior attempts to achieve optical nonreciprocal transmission have included those based on the magneto-optic effect, as discussed, for example, in R. L. Espinola et al, Magneto-Optical Nonreciprocal Phase Shift in Garnet/Silicon-on-Insulator Waveguides, 29 Opt. Lett. 941 (2004). Others attempts include those based on optical non-linearity as discussed, for example, in S. F. Mingaleev, et al., Nonlinear Transmission and Light Localization in Photonic-Crystal Waveguides, 19 J. Opt. Soc. Am. B 2241 (2002). Still other attempts have involved electro-absorption modulation, cholesteric liquid crystals, optomechanical cavities, indirect interband photonic transitions, and opto-acoustic effects.
While many of these attempts have achieved optical nonreciprocal transmission, they have limitations. Specifically, none of these attempts have achieved a CMOS-compatible passive optical diode with a footprint and functionality analogous to p-n junctions, for use at near infrared light. Near infrared light is the wavelength choice for silicon photonics.
There is a need, therefore, for an optical diode, or optical nonreciprocal transmission device, that operates at near infrared light that is passive, and has a reduced footprint and is CMOS-compatible.